The present invention relates generally to wheel position determination in a remote tire monitoring system.
Remote tire monitoring systems have been developed using radio technology to provide centralized tire pressure information to an operator of a vehicle. Such systems typically include a plurality of sending units or transmitters associated with the tires of a vehicle, such as an automobile, truck or other wheeled vehicle, along with a receiving unit. The transmitters measure a tire characteristic, such as tire air pressure, and communicate data corresponding to the tire characteristic to the receiving unit. The receiving unit takes some action in response to the data, such as providing an alarm or providing a display indicative of the tire characteristic for the operator of the vehicle.
In order for the receiving unit to reliably indicate the tire characteristic, the receiving unit preferably associates the tire characteristic data with a tire position on the vehicle. This association is made upon initial installation of tires on the vehicle and must be repeated each time tire position is changed, such as after tire rotation.
U.S. Pat. No. 5,600,301, assigned to the assignee of the present application, discloses a tire pressure monitoring system that includes sending units associated with each tire of a vehicle and a central receiving unit. Each of the sending units includes a respective radio frequency (RF) transmitter that transmits an RF signal, including both an identifier code and an indicator of tire pressure. Additionally, each of the sending units includes a magnet sensor. When the receiving unit is placed in a learn mode, a magnet is used to activate each sending unit of the vehicle in a predetermined order. The receiving unit learns the identifiers associated with the respective tires based upon the sequence of activation of the sending units. This approach has been found reliable in use, but it requires the user to have a suitable magnet for sequentially activating the sending units.
In one patent application assigned to the assignee of the present application, a remote tire pressure monitoring system includes a sending unit for each monitored tire. The sending units transmit RF signals including an identifier and a pressure indicator. A receiver operates in a learn mode in which the receiver associates specific identifiers either with the vehicle or with specific tires. During the learn mode, the vehicle is driven at a speed above a threshold speed and identifiers are associated with either the vehicle or the respective tires of the vehicle only if they persist for a selected number of signals or frames during the learning period. In one example, the tires are inflated with different pressures according to a predetermined pattern and the pressure indicators of the receive signals are used to associate individual tire positions with the respective sending units.
Other techniques for programming a receiving unit with tire position information involve manual entry of the information. This has been done by using a keypad to enter both the tire monitor identification information and tire position information. This has also been done by using a bar code reader to read the tire monitor identification information directly from the tire monitor while still manually entering the tire position information.
The approaches discussed above are not fully automatic and an automatic technique is desired to improve reliability and convenience for the user.